package lion.common;

import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @see org.apache.catalina.util.SessionIdGenerator
 * @author tomcat
 * 
 */
public class SessionIdGenerator {

	public static Logger log = LoggerFactory.getLogger(SessionIdGenerator.class);

	/**
	 * Queue of random number generator objects to be used when creating session identifiers. If the queue is empty when a random number generator is required, a new random number
	 * generator object is created. This is designed this way since random number generators use a sync to make them thread-safe and the sync makes using a a single object
	 * slow(er).
	 */
	private Queue<SecureRandom> randoms = new ConcurrentLinkedQueue<SecureRandom>();

	/**
	 * The Java class name of the secure random number generator class to be used when generating session identifiers. The random number generator class must be self-seeding and
	 * have a zero-argument constructor. If not specified, an instance of {@link SecureRandom} will be generated.
	 */
	private String secureRandomClass = null;

	/**
	 * The name of the algorithm to use to create instances of {@link SecureRandom} which are used to generate session IDs. If no algorithm is specified, SHA1PRNG is used. To use
	 * the platform default (which may be SHA1PRNG), specify the empty string. If an invalid algorithm and/or provider is specified the {@link SecureRandom} instances will be
	 * created using the defaults. If that fails, the {@link SecureRandom} instances will be created using platform defaults.
	 */
	private String secureRandomAlgorithm = "SHA1PRNG";

	/**
	 * The name of the provider to use to create instances of {@link SecureRandom} which are used to generate session IDs. If no algorithm is specified the of SHA1PRNG default is
	 * used. If an invalid algorithm and/or provider is specified the {@link SecureRandom} instances will be created using the defaults. If that fails, the {@link SecureRandom}
	 * instances will be created using platform defaults.
	 */
	private String secureRandomProvider = null;

	/** Node identifier when in a cluster. Defaults to the empty string. */
	private String jvmRoute = "";

	/** Number of bytes in a session ID. Defaults to 16. */
	private int sessionIdLength = 16;

	/**
	 * Specify a non-default @{link {@link SecureRandom} implementation to use.
	 * 
	 * @param secureRandomClass
	 *            The fully-qualified class name
	 */
	public void setSecureRandomClass(String secureRandomClass) {
		this.secureRandomClass = secureRandomClass;
	}

	/**
	 * Specify a non-default algorithm to use to generate random numbers.
	 * 
	 * @param secureRandomAlgorithm
	 *            The name of the algorithm
	 */
	public void setSecureRandomAlgorithm(String secureRandomAlgorithm) {
		this.secureRandomAlgorithm = secureRandomAlgorithm;
	}

	/**
	 * Specify a non-default provider to use to generate random numbers.
	 * 
	 * @param secureRandomProvider
	 *            The name of the provider
	 */
	public void setSecureRandomProvider(String secureRandomProvider) {
		this.secureRandomProvider = secureRandomProvider;
	}

	/**
	 * Specify the node identifier associated with this node which will be included in the generated session ID.
	 * 
	 * @param jvmRoute
	 *            The node identifier
	 */
	public void setJvmRoute(String jvmRoute) {
		this.jvmRoute = jvmRoute;
	}

	/**
	 * Specify the number of bytes for a session ID
	 * 
	 * @param sessionIdLength
	 *            Number of bytes
	 */
	public void setSessionIdLength(int sessionIdLength) {
		this.sessionIdLength = sessionIdLength;
	}

	/**
	 * Generate and return a new session identifier.
	 */
	public String generateSessionId() {

		byte random[] = new byte[16];

		// Render the result as a String of hexadecimal digits
		StringBuilder buffer = new StringBuilder();

		int resultLenBytes = 0;

		while (resultLenBytes < sessionIdLength) {
			getRandomBytes(random);
			for (int j = 0; j < random.length && resultLenBytes < sessionIdLength; j++) {
				byte b1 = (byte) ((random[j] & 0xf0) >> 4);
				byte b2 = (byte) (random[j] & 0x0f);
				if (b1 < 10)
					buffer.append((char) ('0' + b1));
				else
					buffer.append((char) ('A' + (b1 - 10)));
				if (b2 < 10)
					buffer.append((char) ('0' + b2));
				else
					buffer.append((char) ('A' + (b2 - 10)));
				resultLenBytes++;
			}
		}

		if (jvmRoute != null && jvmRoute.length() > 0) {
			buffer.append('.').append(jvmRoute);
		}

		return buffer.toString();
	}

	private void getRandomBytes(byte bytes[]) {

		SecureRandom random = randoms.poll();
		if (random == null) {
			random = createSecureRandom();
		}
		random.nextBytes(bytes);
		randoms.add(random);
	}

	/**
	 * Create a new random number generator instance we should use for generating session identifiers.
	 */
	private SecureRandom createSecureRandom() {

		SecureRandom result = null;

		long t1 = System.currentTimeMillis();
		if (secureRandomClass != null) {
			try {
				// Construct and seed a new random number generator
				Class<?> clazz = Class.forName(secureRandomClass);
				result = (SecureRandom) clazz.newInstance();
			} catch (Exception e) {
				log.error("", e);
			}
		}

		if (result == null) {
			// No secureRandomClass or creation failed. Use SecureRandom.
			try {
				if (secureRandomProvider != null && secureRandomProvider.length() > 0) {
					result = SecureRandom.getInstance(secureRandomAlgorithm, secureRandomProvider);
				} else if (secureRandomAlgorithm != null && secureRandomAlgorithm.length() > 0) {
					result = SecureRandom.getInstance(secureRandomAlgorithm);
				}
			} catch (NoSuchAlgorithmException e) {
				log.error("", e);
			} catch (NoSuchProviderException e) {
				log.error("", e);
			}
		}

		if (result == null) {
			// Invalid provider / algorithm
			try {
				result = SecureRandom.getInstance("SHA1PRNG");
			} catch (NoSuchAlgorithmException e) {
				log.error("", e);
			}
		}

		if (result == null) {
			// Nothing works - use platform default
			result = new SecureRandom();
		}

		// Force seeding to take place
		result.nextInt();

		long t2 = System.currentTimeMillis();
		if ((t2 - t1) > 100)
			log.info("sessionIdGenerator.createRandom,algorithm={},val={}", result.getAlgorithm(), Long.valueOf(t2 - t1));
		return result;
	}
}
